Effects of temperature on the ion-induced bending of germanium and silicon nanowires

Nanowires can be manipulated using an ion beam via a phenomenon known as ion-induced bending (IIB). While the mechanisms behind IIB are still the subject of debate, accumulation of point defects or amorphisation are often cited as possible driving mechanisms. Previous results in the literature on IIB of Ge and Si nanowires have shown that after irradiation the aligned nanowires are fully amorphous. Experiments were recently reported in which crystalline seeds were preserved in otherwise-amorphous ion-beam-bent Si nanowires which then facilitated solid-phase epitaxial growth (SPEG) during subsequent annealing. However, the ion-induced alignment of the nanowires was lost during the SPEG. In this work, in situ ion irradiations in a transmission electron microscope at 400°C and 500°C were performed on Ge and Si nanowires, respectively, to supress amorphisation and the build-up of point defects. Both the Ge and Si nanowires were found to bend during irradiation thus drawing into question the role of mechanisms based on damage accumulation under such conditions. These experiments demonstrate for the first time a simple way of realigning single-crystal Ge and Si nanowires via IIB whilst preserving their crystal structure

Preliminary assessment of the irradiation behaviour of the FeCrMnNi High-Entropy Alloy for nuclear applications

In the search for new nuclear materials with improved radiation tolerance and behavior, the high-entropy alloys (HEAs) have arisen as new candidates for structural components in nuclear reactors due to their suspected superior stability under irradiation. The metallurgical definition of HEAs is any alloy with multiple elements, five or more all in equiatomic compositions. The basic principle is the high mixing entropy of its solid solution lowers the Gibbs free energy giving a strong enhancement of the microstructural stability at low and high temperatures. The objective of this project is to assess the irradiation behaviour of the FeCrMnNi HEA system in order to investigate whether the high entropy effect is responsible for a microstructure with better radiation resistance compared to conventional alloys. In this work transmission electron microscopy (TEM) with in-situ ion irradiation has been used at the MIAMI-1 facility at the University of Huddersfield, UK: a 100 kV ion accelerator coupled with a JEOL JEM-2000FX TEM. This methodology allows the evolution of the HEA microstructure to be studied on the nanoscale during the ion irradiation

Fabrication of bulk delta-phase Zirconium Hydride from Zircaloy-4 for use as moderators in microreactors

The fabrication of bulk delta-phase Zirconium Hydride ($\delta$-ZrH) using Zircaloy-4 as a precursor is herein reported. Characterization using electron-microscopy methods indicate that the fabricated material is of a single-phase. Sn-rich segregation zones have been observed to form as a direct result of the hydriding process. These findings experimentally validate previous \textit{ab initio} calculations on the influence H incorporation in Zircaloy-4 constitutional elements such as Sn, Fe and Cr. The effect of hydriding and Sn segregation on pre-existing Zr(Fe,Cr)$_{2}$ Laves phases is also evaluated. Major implications on the development of moderators for use in microreactors within the nuclear industry are discussed

Perspectives on Novel Refractory Amorphous High-Entropy Alloys in Extreme Environments

Two new refractory amorphous high-entropy alloys (RAHEAs) within the W--Ta--Cr--V and W--Ta--Cr--V--Hf systems were herein synthesized using magnetron-sputtering and tested under high-temperature annealing and displacing irradiation using \textit{in situ} Transmission Electron Microscopy. While the WTaCrV RAHEA was found to be unstable under such tests, additions of Hf in this system composing a new quinary WTaCrVHf RAHEA was found to be a route to achieve stability both under annealing and irradiation. A new effect of nanoprecipitate reassembling observed to take place within the WTaCrVHf RAHEA under irradiation indicates that a duplex microstructure composed of an amorphous matrix with crystalline nanometer-sized precipitates enhances the radiation response of the system. It is demonstrated that tunable chemical complexity arises as a new alloy design strategy to foster the use of novel RAHEAs within extreme environments. New perspectives for the alloy design and application of chemically-complex amorphous metallic alloys in extreme environments are presented with focus on their thermodynamic phase stability when subjected to high-temperature annealing and displacing irradiation

A contamination-free electron-transparent metallic sample preparation method for MEMS experiments with in situ S/TEM

Microelectromechanical systems (MEMS) are currently supporting ground-breaking basic research in materials science and metallurgy as they allow in situ experiments on materials at the nanoscale within electron-microscopes in a wide variety of different conditions such as extreme materials dynamics under ultrafast heating and quenching rates as well as in complex electro-chemical environments. Electron-transparent sample preparation for MEMS e-chips remains a challenge for this technology as the existing methodologies can introduce contaminants, thus disrupting the experiments and the analysis of results. Herein we introduce a methodology for simple and fast electron-transparent sample preparation for MEMS e-chips without significant contamination. The quality of the samples as well as their performance during a MEMS e-chip experiment in situ within an electron-microscope are evaluated during a heat treatment of a crossover AlMgZn(Cu) alloy.Comment: Preprint submitted to Microscopy and Microanalysi

Estudos sobre a perspectiva histórico-cultural de Vigotski

Veresk é uma publicação internacional de Psicologia que se propõe a divulgar trabalhos que examinam e aprofundam o estudo do legado da teoria de Lev Semionovitch Vigotski. Os autores são especialmente convidados a apresentarem seus textos pelos Editores Associados ou pelo Conselho Editorial. Veresk é apresentada tanto no formato impresso, quanto no eletrônico, nas versões em russo, português e inglês. Sua publicação é patrocinada pelo Instituto de Psicologia L. S. Vigotski, da Universidade Estatal de Humanidades da Rússia, pela Faculdade de Educação da Universidade Federal Fluminense, Brasil e pela Faculdade de Ciências da Saúde, do Centro Universitário de Brasília, Brasil.Série VERESK: Cadernos Acadêmicos Internacionais, volume

Detección de Chlamydophila spp. en gatos con problemas oculares y respiratorios

En los últimos años se ha avanzado en el conocimiento de los integrantes del orden Chlamydiales y Chlamydophila felis es uno de los miembros del orden y forma parte de la familia Chlamydiaceae. Este microorganismo, tiene un rol patógeno importante en los felinos domésticos. Produce enfermedad endémica en los criaderos de gatos y podría afectar a otros felinos. Nuestro propósito fue detectar Chlamydophila spp en gatos domésticos con sintomatología respiratoria y ocular en la ciudad de La Plata, Argentina. Se tomaron muestras de animales enfermos, las que se analizaron utilizando la detección de Lipopolisacárido Clamidial común (LPS) por la técnica de Elisa y la inoculación en huevos embrionados libres de patógenos específicos( SPF ) para propagación de Chlamydophila felis. La detección y aislamiento de Chlamydophila spp fue elevada en los animales investigados. Los más jóvenes fueron lo mas afectados, no obstante todos los felinos fueron susceptibles, sin importar la edad. Se pudo verificar el rol endémico de Chlamydophila spp en los gatos domésticos de nuestro medio. Se sugiere un posible rol zoonótico de este microorganismos en personas que interactúan con estos animales. Se requiere de técnicas especiales para determinar con certeza al agente infeccioso en gatos domésticos.Facultad de Ciencias Veterinaria